The invention relates to a process and an installation for sintering metal-containing materials, such as for example iron ores or manganese ores, in particular oxidic or carbonaceous ores, on a sintering machine with sintering waste gas return.
The sintering of metal-containing materials, such as for example iron ores or manganese ores, in particular oxidic or carbonaceous ores, takes place by means of sintering machines. After charging the sinter mix, which comprises the metal-containing material, revert material, solid fuel, fluxes, etc., onto the sintering belt of the sintering machine, the sinter mix is ignited on its surface in an ignition furnace. Subsequently, oxygen-containing gases are passed through the sinter mix as process gas, whereby the sintering front migrates from the surface of the sinter mix in the direction of the surface of the sintering belt. The gases used as process gas are, for example, fresh air, waste air from a sinter cooler, air used for pre-drying the sinter mix, a mixture of a number of these gases, or a mixture of one or more of these gases with tonnage oxygen. At the same time, the sintering belt is moved from the charging point in the direction of the discharging point. During the transport on the sintering belt, the entire sinter mix is sintered through and leaves the sintering belt at the discharge point as hot finished sinter. The hot finished sinter is cooled in a downstream sinter cooler. Sintering machines may be designed for example in the form of traveling grate sintering machines, in which the process gas is sucked through the sinter mix by negative pressure being applied to the suction boxes lying under the sintering belt by means of blowers.
During normal operation, the temperature and oxygen content of the sintering waste gas occurring change along the sintering belt. The temperature of the sintering waste gas increases along the sintering belt. The oxygen content of the sintering waste gas initially decreases along the sintering belt, to increase again after reaching a minimum. Usually, the temperature of the sintering waste gas in the front, first portion of the sintering belt is below 100° C. and increases toward the rear portion to over 300° C.
The process gas is sucked through the sinter mix by means of suction boxes positioned under the sintering belt and the sintering waste gas produced during this passage is collected and conducted away. Since the sintering operation requires large amounts of process gas, large amounts of sintering waste gas occur. The sintering waste gas contains, inter alia, evaporated water from the sinter mix, CO2 and CO from the sometimes incomplete combustion of the fuel and calcination processes, also sulfur oxides SOx, from the combustion of sulfur contained in the fuel or ore, as well as nitrogen oxides NOx, dioxins, furans and dust. Before the sintering waste gas can be released into the environment as waste gas of the sintering machine, the removal of pollutants is therefore necessary to minimize the environmental impact. Reducing the amount of waste gas to be discharged from a sintering machine or the pollutant burden contained in the waste gas facilitates waste gas cleaning.
It is already known to reduce the amount of waste gas and the pollutant burden contained in the waste gas by returning part of the sintering waste gas to the sinter mix as process gas. One effect of this is that the amount of process gas that is introduced into the sintering machine from outside is reduced and another effect is that better use is made of the oxygen contained in it.
So, for example, JP-53-004706 describes partial return of the sintering waste gases to the sinter mix, the cold sintering waste gas from the front, first portion of the sintering belt being conducted to the hot sintering waste gas from the rear, third portion before both gases are unified. This means, however, that the transporting distance that the cold sintering waste gas has to cover before it is unified with the hot sintering gas is very long. This also means that the acid formed by the nitrogen oxides NOx, sulfur oxides SOx and water vapor contained in the sintering waste gases will condense out in this long stretch over which they are conducted as a result of the temperature falling below the dew points of the acids. The acids condensing out are highly corrosive.